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Daily Coronal Images Available from NSO/SP (1Jun92)
(from NSO, NOAO Newsletter No. 30, 1 June 1992)

Observations are made at the National Solar Observatory at Sacramento
Peak with the Fisher-Smartt Emission Line Coronal Photometer (ELCP).
This instrument photoelectrically records the solar corona when fed
with the John W. Evans Solar Facility 40-cm Coronagraph.  It operates
at high precision due to its ability to subtract the sky background
from the signal in emission lines through use of a lock-in amplifier
oscillating at a rate of 100 kHz between the continuum and lines at
637.4 nm (Fe X), 530.3 nm (Fe XIV) and 569.4 nm (Ca XV), which are
formed at approximate temperatures of 1, 2 and 3 MK, respectively. A
1.1 arcmin aperture is scanned around the limb daily from 1.15 to 1.45
solar radii for Fe XIV, 1.13 Ro for Ca XV and 1.15 Ro for Fe X. The
output of the ELCP is sensed by a photomultiplier, digitized and
recorded every 3 degrees of latitude. Absolute intensities in
millionths of the brightness of the center of the disk at each
wavelength are obtained by calibrating the system through a neutral
density filter. All Fe X, Ca XV and the 1.45 radius Fe XIV scans are
scaled to have at least one absolute zero intensity data point. Fe XIV
scans at other radii are adjusted by the amount subtracted from the
1.45 radius scan.

The pseudo-full-disk maps are produced by joining together 15 days of
1.15 Ro (Fe XIV) or 1.13 Ro (Ca XV) data from the East or West limbs
into a synoptic map and projecting it onto a sphere.  The most recent
scan is at the beginning of the map, and the data on the central
meridian are from seven days prior to the date of the map. Data are
incremented from the central meridian at 12.857 degrees per day.
West-limb maps, which show the far side of the Sun on the day they are
produced, have been given an effective date two weeks into the future,
so that they may be compared with East-limb maps of the same date. Maps
are currently only produced for Fe XIV and Ca XV and are normally
available for each Monday through Friday, excluding holidays.

A brief synopsis of how to obtain the images is given here. Map file
names are ion.mmddyyl, where ion is fexiv or caxv, mm is the month, dd
is the day, yy is the year, and l is the limb from which the data are
taken (e or w).

SPAN/DECnet procedure (for VAX VMS users): to get a directory listing
(Caution: there are many files!):
     dir 5355::ga0:[ftp.spcm.fexiv or caxv]
to get the readme file:
     copy 5355::ga0:[ftp.spcm]readme localname
to copy a file:
     copy 5355::ga0:[ftp.spcm.fexiv or caxv]filename localname

Representative Internet procedure for copying data: You type:
     ftp draco.tuc.noao.edu (or ftp 140.252.1.5)
when connected, respond with login as:
     anonftp
use as a password:
     guest
change the directory to spcm:
     cd spcm
copy the readme file:
     get readme
enter a data directory:
     cd fexiv or caxv
to get a directory listing (Caution: there are many files!):
     dir
or copy the data using:
     get filename
     bye

For further information, contact thenry or raltrock at NOAO:: or noao.edu.

Dick Altrock

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